The American student Amanda Knox broke her silence in an Italian court yesterday, telling judges and jury that she took no part in the killing of her flatmate Meredith Kercher and was confident of being cleared. "I am innocent," she rose to tell the Perugia court in fluent Italian. "I have faith the truth will come out."

Knox, 21, took advantage of her right under Italian law to address the court, as seven of Kercher's fellow British exchange students lined up to describe Knox's "strange" behaviour the day Kercher was found fatally stabbed and lying in a pool of blood on her bedroom floor.

Knox and her former boyfriend Raffaele Sollecito, both on trial for the murder, had "kissed and joked" at Perugia's police station, said Robyn Butterworth, 23. "There was laughter. She stuck her tongue out at Raffaele. They moved their chairs. She put her feet up on him, they were kissing and cuddling."

A second witness, Amy Frost, thought Knox had "gone crazy," as she waited with Sollecito and the English students to be interviewed by the police.

Both defendants deny the charges. Knox told investigators she returned from a night at Sollecito's flat in Perugia on 2 November 2007 to find Kercher's bedroom door locked and bloodstains in the bathroom, where she took a shower.

Knox did not enter Kercher's bedroom when the door was finally opened in the presence of the police, but Butterworth said that when a second British friend, Natalie Hayward, commented at the police station that she hoped Kercher had not suffered, Knox replied: "What do you think? She fucking bled to death."

Taking the stand, Hayward said Knox explained she had been given a description of Kercher's corpse by Filomena Romanelli, who shared the Perugia house with Kercher and Knox. But then, speaking to her stepfather on the phone, "Knox said 'I found her in the cupboard and she was covered in a blanket,' which confused us," recalled Hayward.

Knox's father, Curt, told journalists before the session it was natural that Knox had claimed to know about the state of Kercher's body: "What is lost here is that there were six people there talking about it, both outside the house in the car to the police station," he said.

Prompted by the prosecutor, Butterworth said Kercher had criticised Knox for leaving their shared bathroom dirty, and had been "uncomfortable" about Knox leaving out a washbag containing contraceptives and a vibrator. Knox said the vibrator was a "joke" gift from a friend.

The British students described their final evening with Kercher, watching a video, eating pizza and "talking about boys from home".